1. Field of the Invention
The present invention relates to a detergent composition having an excellent effect of keeping clothes from yellowing. More particularly, the invention relates to a detergent composition containing citric acid or its salt and isocitric acid or its salt and having an excellent effect of keeping clothes from yellowing by iron components contained in the washing water.
2. Prior Art
Recently, the use of polyphosphates which have been used as main builder for detergents for clothes has been reduced sharply for fear of eutrophication of a closed water system caused by them, and instead phosphate-free detergents are now mainly used. Although water-insoluble zeolite is mainly used as builder for the phosphate-free detergents, its building effect is yet unsatisfactory and, in addition, the zeolite poses problems during the production and use thereof because it is insoluble in water. Under these circumstances, intensive investigations are now being made for the purpose of finding builders other than the above-mentioned zeolite for the phosphate-free detergents.
The properties required of the builders include a capacity of softening hard water, buffer capacity, dispersing capacity, biodegradability and safety and, in addition, a low cost is also required. The builders now attracting attention are citrates in addition to NTA (nitrilotriacetates) etc. The citrates are capable of complexing calcium and magnesium ions and have satisfactory biodegradability and safety.
However, a detergent containing a citrate as a main builder has a defect that it causes yellowing of clothes due to iron contained in the washing water to an extent higher than that caused when a detergent containing an ordinary builder is used. According to investigations now under way on the yellowing of clothes due to ions contained in the washing water, the iron content of tap water used in the washing of clothes seems to be on a relatively high level in homes having their own water reservoirs which are now increasing in number as the apartment houses and tall dwelling buildings are increasing. When such tap water is repeatedly used in washing, clothes are gradually yellowed by the effect of iron [see J. Jap. Res. Assoc. Text. End-uses, 17 (8), 294-300 (1976)].